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My Phone has blank back surface is that normal? Help me!
Welcome to the community!
Can you please elaborate? Do you mean the screen is blank or dark?
Let me know 
The blank on the phone's back side
Yes not the screen. There is swelling at the back of my Phone. I'm using xa1 ultra.
@Blankproblem wrote:Yes not the screen. There is swelling at the back of my Phone. I'm using xa1 ultra.
Wow, what? Swelling?
STOP USING YOUR SMARTPHONE!
Disconnect it from external power, turn it off and then contact your local Sony Customer Care Team, immediately!
A "swelling" battery or a smartphone that is "swelling" usually means that the battery is likely faulty and in some cases, could catch fire or explode!